A fuel cell is a type of device that generates electricity by electrochemically oxidizing a fuel such as hydrogen and methanol to extract electrical energy. Recently, a fuel cell has attracted attention as a clean energy supply source. Depending on the type of electrolyte used, fuel cells are classified into: phosphoric acid type, molten carbonate type, solid oxide type, polymer electrolyte type, and so forth. Among these, the polymer electrolyte fuel cell (PEFC) is a type of fuel cell including a membrane electrode assembly (MEA) in which electrodes are disposed respectively on both surfaces of an electrolyte membrane. The polymer electrolyte fuel cell (PEFC) generates electricity when hydrogen (fuel gas) is supplied to one surface of this membrane electrode assembly (MEA) and oxygen (oxidizing gas) is supplied to the other surface. Since having a power density equivalent to that of an internal combustion engine, the PEFC is now being researched extensively for its practical use as a power source of electric vehicles and the like.
Various types are proposed in a method of packaging an MEA, such as stack type, pleat type, and hollow fiber type. Among these, fuel cells of the stack type are widely used in which sheet-shaped MEAs are stacked one above the other while being isolated by sheet-shaped separators. In such a stack type fuel cell, seal members are provided between the MEA and the separator stacked on each other and between the separators to thereby hermetically seal the fuel gas and the oxidizing gas inside the fuel cell.
A stack type fuel cell described in JP-A 2006-107862 has a sealing structure in which an adhesive is used as a seal member. The adhesive has an improved adhesion as a result of direct application of the adhesive to a base member of a metal separator with no surface treatment performed on a surface of the separator where the adhesive is applied.